The present invention relates generally to a heating, ventilating, and air conditioning system. More particularly, the present invention relates to a method and system for controlling an economizer in a heating, ventilating, and air conditioning system.
Heating, ventilating, and air conditioning (HVAC) systems are used in both warm and cold climates to control the environment, including the temperature, within a building or other enclosure. HVAC systems typically include a heating unit for warming cold air and a cooling unit for cooling warm air. A fan pushes or pulls air over the heating or cooling unit and through a supply duct to the enclosure to condition the air within the enclosure. Air is circulated back to the heating or cooling units from the enclosure through a return duct. The HVAC system may also include an outdoor air damper, or economizer, that can be modulated to allow varying amounts of outdoor to mix with the air in the return duct to provide fresh air to the enclosure.
HVAC systems can be used to condition the air in a building of different sizes. Large buildings are often divided into a series of zones that are conditioned by the same HVAC unit. Each zone may include a thermostat or similar device, to sense and help regulate the condition of the air within the particular zone. Such a thermostat allows a user to select a desired temperature or temperature range for each of the individual zones.
In many cases, a single HVAC unit conditions the air within a number of different indoor spaces or zones. The air conditioned by the HVAC unit is fed into a main supply duct that subdivides into a network of smaller supply ducts that supply air to each individual space or zone. In some variable air volume (xe2x80x9cVAVxe2x80x9d) systems having multiple zones, an air damper is placed in some or each of the smaller supply ducts leading into each individual zone. When the thermostat and/or controller for a zone determines that the temperature of the air in that zone is within the selected temperature range, the control for the system modulates the air damper to reduce or stop the amount of conditioned air entering the respective zone. Similarly, when the thermostat and/or controller for a zone determines that the temperature of that zone is outside of the selected temperature range, the damper is modulated to increase the flow of air into the zone.
When the temperature of a number of the individual zones is brought within the range selected for the particular zone and the dampers leading to many or each of the zones are closed or reduced, the fan continues to push air into the supply duct causing the pressure in the main supply duct to increase. Often, a bypass duct connects the supply duct with the return duct to allow air to circulate and relieve this pressure. The bypass duct usually includes a damper to control the amount of air circulating through the bypass duct. However, when air circulates from the HVAC unit through bypass duct and back to the HVAC unit, the returned air can become very warm or very cold, depending on the current operating state of the HVAC unit. Exposing the components of the HVAC unit to such very warm or very cold air can damage the unit, resulting in equipment failures and increased warranty costs for the components.
In light of the foregoing there is a need for a method and system for moderating the temperature of air circulating in a zoned HVAC system when the requirements of a number of the individual zones are satisfied and the return air becomes too hot or cold.
Accordingly, the present invention is directed to a method and system for maintaining the temperature of air returned to a heating, ventilating and air conditioning unit within a preselected, safe range. This method and system varies the opening of the economizer, based on a number of sensed parameters, including the temperature of supply air leaving the HVAC unit and the temperature of outside air. The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a system for conditioning air, preferably in a plurality of zones. There is provided a heating, ventilating, and air conditioning (HVAC) unit that has an economizer that can introduce selected amounts of outdoor air into the HVAC unit. The HVAC unit provides conditioned air to each of the plurality of zones. A supply air duct connects the HVAC unit to each of the plurality of zones and a return air duct connects each of the plurality of zones to the HVAC unit. According to the invention, a temperature sensor senses a temperature representative of the air returned to the HVAC unit and another temperature sensor for sensing the outdoor temperature. A main control, preferably incorporated into or adjacent the HVAC system, modulates the economizer based on at least these sensed parameters, to regulate the amount of outdoor air entering the HVAC unit when the temperature of the air returned to said unit is excessively cold or excessively warm.
In another aspect, the invention is directed to a control system for i an economizer in a heating, ventilating, and air conditioning unit in a system preferably having a plurality of zones. Each of the plurality of zones are connected to the HVAC unit by a supply duct and a return duct. The control system includes a temperature sensor that senses a temperature representative of the air that is returned to the HVAC unit. A main control modulates the economizer to regulate the amount of outdoor air entering said unit when the temperature of the air returned to said unit is excessively cold or excessively warm.
In yet another aspect, the invention is directed to a method of determining an amount of outdoor air introduced into an air conditioning system, preferably having a plurality of zones. The method involves the steps of operating a heating, ventilating, and air conditioning unit to condition air. A selected amount of conditioned air is supplied to each of the plurality of zones from the HVAC unit through a supply duct. Air is returned to the HVAC unit through a return duct. A temperature representative of the air returned to the HVAC unit is sensed. The economizer is modulated to adjust the amount of outdoor air introduced to the HVAC unit depending upon the sensed temperature of the air returned to the HVAC unit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.